The present invention relates to a catalyst and process for the dimerization of olefins. More specifically, the invention relates to a new method for the preparation of 4-methyl-1-pentene.
The compound 4-methyl-1-pentene is useful as a monomer or as a comonomer in the production of polyolefins. Typically, 4-methyl-1-pentene is produced via the catalytic dimerization of propylene. Commonly employed catalysts include those containing alkali metals or nickel. Low-selectivity catalysts include thorium nitrate, WCl.sub.6, titanium, aluminum alkyls, such as cerium acetylacetonate/aluminum alkyls and certain mixtures of these. Alkali metal catalysts are numerous, but are disadvantageous in that they require high operating temperatures and pressures. Catalysts previously employed for the preparation of 4-methyl-1-pentene via propylene dimerization are all unsatisfactory to the extent that they are not as selective as would be desired. While selectivities to 4-methyl-1-pentene of up to 93 percent have been reported (Chemical Abstracts, 100:102722n) using a Na/K-based catalyst, even this is unsatisfactory in view of the difficulty and expense involved in separating 4-methyl-1-pentene from the commonly coproduced C.sub.6 olefin and C.sub.6 alkane by-products.
Bis(pentahaptopentamethylcyclopentadienyl) (allyl) neodymium and bis(pentahaptopentamethylcyclopentadienyl) (allyl) lanthanum are reported by G. Jeske, et al., J.A.C.S., Vol. 107, pp. 8091-8103 (1985). When reacted with propylene, these materials yield only trace amounts of oligomers with no significant selectivity to 4-methyl-1-pentene. Similarly, bis(pentahaptopentamethylcyclopentadienyl) (allyl) lutetium is proposed as an intermediate in the reaction of bis(pentahaptopentamethylcyclopentadienyl) (methyl) lutetium with propylene by P. L. Watson, et al., J.A.C.S., Vol. 104, pp. 6471-6473 (1982). The products of this chemistry are trace oligomers with no significant selectivity to 4-methyl-1-pentene.
Tris(pentahaptocyclopentadienyl) (allyl) uranium and tris(pentahaptocyclopentadienyl) (allyl) thorium are reported by T. J. Marks et al., J.A.C.S., Vol. 95, pp. 5529-39 (1973) and in Vol. 98, pp. 703-10 (1976), respectively. Pentahaptopentamethylcyclopentadienyltris-(allyl) uranium is described in Organometallics, Vol. 2, pp. 963-9 (1983).
U.S. Pat. No. 3,994,945 discloses uranium(IV) tetraallyl compounds and certain halide derivatives thereof. The halide compounds are reported to be useful as catalysts in the stereospecific polymerization of diolefins.
U.S. Pat. No. 3,816,372 discloses uranium(IV) complexes containing metal to carbon .sigma. bonds. Ligands such as allyl, cyclobutadienyl and cyclopentadienyl are taught to be coordinated to the metal by .pi. bonds. The compounds are disclosed as being useful in the oligomerization of olefins and diolefins, and in the insertion reaction of neutral molecules such as CO and NO.
In view of the deficiencies of prior art methods, it would be desirable to have a catalytic process which would provide improved selectivity to 4-methyl-1-pentene.